Relaxation of ferromagnetic ordering in pseudoternary superconductors

Abstract

The low-temperature phase diagrams of the superconducting and magnetic pseudoternary systems ${\mathrm{Ho}}_{1.2\ensuremath{-}x}{R}_{x}{\mathrm{Mo}}_{6}{\mathrm{S}}_{8}$ with $R=\mathrm{Tb}$ and Er have been determined by means of low-frequency ac magnetic susceptibility and neutron-diffraction measurements and are qualitatively described with a molecular-field model. A very slow transition from a ferromagnetic to a superconducting state was observed at 100 mK in Ho-rich ${\mathrm{Ho}}_{1.2\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Mo}}_{6}{\mathrm{S}}_{8}$ compounds with $x$ values between 0.2 and 0.4. This unusual behavior can be interpreted in terms of the similarity of the free energies of the antiferromagnetic superconducting and normal ferromagnetic states at very low temperatures. Neutron-diffraction measurements on a ${\mathrm{Ho}}_{1.0}$${\mathrm{Tb}}_{0.2}$${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$ sample revealed the presence of a long-wavelength oscillatory magnetic phase which coexists with superconductivity, similar to the one that occurs in pure ${\mathrm{Ho}}_{1.2}$${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$.